Planks (panels) or boards are employed in floorings. For example, planks are cut from a large laminated flooring board or substrate to make it easy for shipping and handling by installers and then the planks are later put together to cover a floor. Planks can be provided with multiple edges, and at least one of the edges can have a bevel surface that can be formed by cutting away one or more edges, as described in U.S. Pat. No. 6,786,019, which is incorporated herein in its entirety by reference. The edges can have a tongue and groove profile as well, for example as described in International Patent Publication No. WO 97/47934, which is incorporated herein in its entirety by reference. The edges and/or other parts of the floor plank can have one or more areas simulating grout, mortar, borders, or other depressed or indented areas of a pattern by embossing or by routing, or by cutting or any combination thereof. The top face of the laminated flooring can have a surface décor or a face pattern, for example, as described in U.S. Pat. No. 6,786,019.
Several methods of providing a decorative design onto the surface of a bevel edge have been used. These include emboss bevel by registration, thermo-foil transfer printing and vacuum coating and/or roll coating (pigmented coating).
In the emboss bevel by registration process, the same pattern covers the entire surface and edges of the laminated flooring. Only the edges are depressed to form into the bevel surfaces by the embossing plate that is aligned to the edges of the board during the pressing operation. The difficulty of this process is to precisely line up printed paper that carries the design, to the edges of the embossing plate as well as to cut the individual embossed bevel plank out of the whole pressed board. This process is typically done by a smaller press in a highly manual and intensive labor involved operation. Even with that, the process still produces a higher rate of off-goods due to poor registration during pressing and the rip-cutting operation. The manufacture cost of making bevel edges from this process is generally high.
In the more common thermo-foil transfer printing process, a pre-formed thermo-foil is used to transfer a pre-print design onto a bevel surface. The thermo-foil is prepared as a thin multi-layered film construction. The construction involves a Mylar carrier film (Mylar is a thin, strong polyester film that is typically used in packaging, insulation, recording tapes or photography), an easy release layer, a wear layer such as an acrylic layer, a gravure printed decorative layer (gravure is a printing process using multiple engraved cylinders to create a design), or a pre-printed paper, and a heat activated adhesive layer.
In the process of transfer printing by thermo-foil, the thermo-foil is passed between a heated silicone rubber roll and the surface of the bevel edge such that the thermo-foil is aligned. This allows the hot silicone rubber roll to contact the Mylar carrier side of the thermo-foil and the adhesive to contact the surface of the bevel edge. The decorative layer on the thermo-foil is then transferred to the surface of the bevel edge by means of appropriate temperature and pressure for an appropriate contact time by a heated pressing roll. The carrier film is then separated by pulling it from the product and rolling it up on a collection roll.
In such a process, a KURTZ KTF 70® machine, for example, can be used which typically operates at 240-270° C. on the silicone rubber belt and the line speed is about 50-60 meters per minute, resulting in a contact time of about 0.3 second. The amount of heat applied on the pressing roll, the dwelling time of pre-heating the bevel surface, the transfer of the decorative layer or pre-printed paper, and the pressure of the roll are factors that control the speed and image of the design being transferred.
The thermo-foil transfer printing on a bevel surface is complicated since it involves at least a three step process, which requires firstly forming the thermo-foil through a complicated gravure printing process and then secondly slitting the printed roll into multiple 7-8 mm wide coils; many small diameter coils are then spooled into a large diameter size coil for production used. Lastly, the coil is then transferring the pre-formed thermo-foil onto the bevel surface. During the gravure printing process, matching the color and pattern of a chosen sample is required which is also a daunting and time consuming step. This is usually accomplished through multiple trials and errors. Adding to the complexity is the long lead time and high cost associated with the gravure printing process. The steps involved are pre-press preparation; design proofing, and cylinders engraving etc. before running the printing operation.
Additionally, after matching the color and pattern, manufacturers typically need a large quantity of the thermo-foil in order to justify the efficiency of the operation and to lower the cost of making the end product. Therefore, the manufacturer typically carries a significant amount of inventory of the thermo-foil.
Another draw back of transfer printing thermo-foil onto bevel surfaces of laminated floorings is the waste factor, which can ultimately increase the cost of the manufacturing of the laminated floorings. The width of a pre-formed thermo-foil is usually 8-9.5 mm but the typical width of a bevel of laminated flooring that needs to be covered by the thermo-foil is 1.0 to 2.0 mm. The effective utilization of the thermo-foil is only 10-20% and the rest is wasted material. As a result, the waste of the thermo-foil in covering the bevel surface is extremely high.
There is yet another drawback in using transfer printing thermo-foil. The core of laminated flooring which at least in part forms the bevel surface can be made from different materials, such as very hard core materials. Certain hard core materials, such as high density fiberboard (HDF), can make the conventional printing processes of the bevel surface cumbersome and problematic. For example, after beveling a plank for the laminated flooring, the bevel surface may not be sufficiently smooth due to the rough surface caused by micro-fibers in a HDF or residual shaving dusts on the surface. This can significantly and negatively affect the adhesion of the thermo-foil on the bevel surface.
The biggest drawback in using transfer printing thermo-foil is that it is not applicable for decorating grout, mortar and border areas of a plank/tile which have the recessed areas away from the edge, such as in the middle of the panel and/or the recessed depth is relatively shallow in relationship with the non-recessed areas. It is very difficult to transfer the printing thermo-foil into the recessed areas with enough pressure for good adhesion and also to control the foil precisely going to the recessed areas without transferring onto the boundary of the flat, non-recessed surface of the panel.
In vacuum coating, a vacuum coating machine is used and the machine is based on a vacuum die. The vacuum die is constructed to have an identical shape of what is to be coated, so that it contours to the surface of the part to be coated. This is a significant limitation of the process in itself. A color coating liquid is fed through a port in the center of the die that floods the surface to be coated and decorated. Surrounding the die are orifices under vacuum to remove excessive colored coating liquids. A thin layer of coating results and covers the surface to be decorated.
The support system for vacuum coating that surrounds the die is a chamber that contains the color coating liquid and vacuum equipment in order to keep the die under vacuum. This system allows only low viscosity liquid coating to be applied. The typical viscosity of the liquid is 400 to 800 cps. The coating weight is 0.4 gram per foot for a particular tongue and groove joint system. The coating liquid is usually applied at 60 psi vacuum with 50% recycle supply and with a line speed of 70 fpm.
In roll coating, basic coating machines such as a 2 roll coater, differential roll coater, reverse roll coater etc. are usually used to apply a coating liquid on a surface of the bevel edge. A layer of a coating liquid metered by the coater machine is applied on the bevel surface. The viscosity of the coating for this application is typically higher; the thickness of the coating on the bevel surface is therefore thicker and tends to spread over the edges of the decorative surface. The appearance of the coated bevel does not look realistic at all even though the goal is to resemble real hard wood flooring.
Both the vacuum coating and roll coating are limited in terms of the “design” that can be placed on a surface that is to be coated. Such methods can be simply categorized as “pigment coating” as they relate more to coating a surface instead of providing a more complicated pattern, such as a “design” onto a surface.
Accordingly, there is a need to eliminate carrying an inventory of thermo-foils. There is also a need to provide short runs of printing and/or a higher speed of printing, with better images and performance. There is also a need to provide versatility in color and pattern selection to match the color and pattern of the surface décor or face design of the laminated flooring. There is also a need to provide a method of printing without limitations on a printed surface, in order to accommodate both a smooth surface and a rough surface. Thus, there is a need to print the surfaces of bevel edges as well as tongue and groove joints with the color and the pattern matching the décor surface of the laminate. Additionally, there is a need to provide better adhesion and abrasive resistance properties for decorating a bevel surface. There is an additional need to use an environmental friendly radiation curable, 4 processing color (CMYK) ink system to achieve desirable speed and property. There is a need to use an ink jet printing system with 4 printing heads to achieve flexibility and versatility in printing any color and any pattern. There is an additional need to align multiple printing heads in a straight line to maximize the printing quality and image of the design. There is also a need for mounting printing heads at a 45 degree angle (or other angle) facing upward to the transporting direction of the bevel edges of the panel. There is a need to print all bevel edges around the panel in line with the same or similar speed as the step of profiling the tongue and groove connecting joint. There is also a need to use piezo ink jet printing heads to optimize the droplet placement and size. There is a need to change meniscus/pressure regulation to control ink jet printing reliability. There is a need to set the throw distance of the printing heads at a safe gap to avoid head strikes by the moving panel. There is also a need for better material utilization and cutting down of the waste of materials. There is also a need for decorating a bevel surface with a minimum space required for printing and curing equipment. There is also a need for changing the color and the pattern of the bevel surface on the fly (without shutting down the line) during the operation. Flexibility in the manufacturing process and lowering of costs are also needed in a method and system for printing patterns and designs on bevel surfaces of laminated flooring.